1. Field of the Invention
The present invention relates to a shadow mask, and more particularly, to an organic electroluminescent device for fabricating a shadow mask. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for minimizing shadows and uniformly depositing an organic compound, thereby fabricating a high-resolution organic electroluminescent device.
2. Discussion of the Related Art
An electroluminescent device is being viewed as a next generation flat display device for its characteristics of a wide viewing angle, a high aperture ratio, and a high chromaticity. More specifically, in an organic electroluminescent (EL) device, when an electric charge is injected into an organic luminescent layer formed between a hole injection electrode and an electron injection electrode, the electron and the hole are paired to each other generating an exciton, the excited state of which falls to a ground state, thereby emitting light. Thus, the organic electroluminescent device (ELD) can be operated at a lower voltage, as compared to other display devices.
Depending upon the driving method, the organic ELD can be classified into a passivation ELD and an active matrix ELD. The passivation ELD is formed of a transparent electrode on a transparent substrate, an organic luminescent layer on the transparent electrode, and a cathode electrode on the organic luminescent layer. The active matrix ELD is formed of a plurality of scan lines and data lines defining a pixel area on a substrate, a switching device electrically connecting the scan lines and the data lines and controlling the electroluminescent device, a transparent electrode (or anode) electrically connected to the switching device and formed in the pixel area on the substrate, an organic luminescent layer on the transparent electrode, and a metal electrode (or cathode) on the organic luminescent layer. Unlike the passivation ELD, the active matrix ELD further includes the switching device, which is a thin film transistor (TFT).
FIG. 1 illustrates a cross-sectional view of a general organic electroluminescent device. Referring to FIG. 1, an indium-tin-oxide (ITO) electrode 12 is formed on the substrate 11 in a striped form, and insulating layer patterns 15 and barrier ribs 16 are serially formed on the ITO electrode 12. In addition, an organic luminescent layer 13 is formed on the ITO electrode 12, and an anode electrode 14 is formed on the organic luminescent layer 13. Herein, the organic luminescent layer 13 is formed in the pixel area on the ITO electrode 12 by using a shadow mask.
FIGS. 2A and 2B illustrate plane views of a related art shadow mask for fabricating an organic electroluminescent device. Referring to FIG. 2A, the related art shadow mask 20 includes a plurality of slots 21. Each of the slots 21 acts as a pattern for depositing an organic luminescent substance and are aligned with the striped ITO electrodes 12. However, the shadow mask 20 is disadvantageous in that the shadow mask 20 can be easily deformed by stress. The shadow mask 30 shown in FIG. 2B includes a plurality of bridges 32 formed between each slot 31 in order to prevent deformation caused by stress.
The above-described related art shadow masks 20 and 30 result in shadows, as shown in the cross-sectional view of FIG. 3. In other words, the vertical cross-section of the shadow mask 20 and 30 interrupts organic compounds from being deposited on the ITO electrode 12, which is adjacent to the edge of each slot 21 and 31, thereby forming a dead area wherein the desired thickness of the organic compound is not deposited. For such reasons, it is difficult to fabricate a high-resolution electroluminescent device.